1. Field of the Invention
This invention relates to making junction-type semiconductor devices.
2. Description of the Prior Art
Methods are known for making junction-type semiconductor devices (transistors, diodes, etc.) that involve the introduction, into a suitable wafer material such as silicon, germanium, gallium arsenide, gallium phosphide, indium antimonide, or silicon-germanium alloy, of a controlled, small quantity of a dopant material. There are known N-type dopant materials, such as phosphorus pentoxide or arsenic, antimony, iron, or cobalt. There are known P-type dopant materials, such as boron nitride, boric acid, indium, methyl borate, and gallium.
In the early days of the making of such devices, the dopant was usually introduced onto or into the wafer by using either an epitaxial-growth process that involves deposition of vaporized wafer material containing a relatively small number of atoms of dopant material, or a gas-phase diffusion process. Such procedures are, of course, both time-consuming and costly.
Somewhat more recently, there has been developed the practice of mixing a dopant material with an organic binder to form a slurry and then painting the slurry onto the surface of the wafer, which is then heated in a furnace to permit the dopant to diffuse into the wafer. The hand-painting step is tedious, and it sometimes results in non-uniformity of the distribution of the dopant within the wafer after the diffusion step. When this happens, the quality of the junction obtained is adversely affected, sometimes to the extent that the treated wafer must be discarded.